Method and apparatus for mapping and de-mapping in an optical transport network

ABSTRACT

The embodiments of the present invention disclose method and apparatus for mapping and de-mapping in an optical transport network, where the mapping method includes: constructing an Optical Channel Data Tributary Unit (ODTU) according to an amount M of time slots of a High Order Optical Channel Payload Unit (HO OPU) to be occupied by a Low Order Optical Channel Data Unit (LO ODU); mapping the LO ODU to a payload area of the ODTU in a M-byte granularity; encapsulating overhead information to the overhead area of the ODTU; and multiplexing the ODTU, which has been mapped the LO ODU and encapsulated with the overhead information, to the HO OPU, so as to provide a high-efficient and universal mode for mapping the LO ODU to the HO OPU.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of the Chinese Patent ApplicationNo. 200910106028.2 filed on Mar. 9, 2009, which is incorporated hereinby reference in its entirety.

FIELD OF TECHNOLOGY

The present invention relates to the field of communicationtechnologies, and particularly, to a mapping technique in an opticaltransport network.

BACKGROUND OF THE INVENTION

With the quick development of communication technology, the OpticalTransport Network (OTN) with advantages of flexible scheduling andmanagement of large capacity services is increasingly becoming a majortechnology of the backbone transport network. In the OTN, the clientdata is encapsulated into an Optical Channel Payload Unit (OPU), someoverhead (OH) is added to the OPU to constitute an Optical Channel DataUnit (ODU), some OH and Forward Error Correction (FEC) is added into theODU to constitute an Optical Channel Transport Unit (OTU), and isfinally transmitted in the form of OTU.

With the rapid development of data service, more and more clients adoptEthernet technology as the physical interface at the client side. It isforeseeable that in the coming years, the Ethernet service will keep acontinuous high-speed growth. However, the current OTN technology isdesigned based on speech service such as synchronous digital hierarchy(SDH), and cannot well support the development trend of data servicelike Ethernet, thus studies are gradually carried out on the nextgeneration of OTN network (NG OTN). The NG OTN is required to not onlymeet the requirements of services newly appear, but also bear thecurrent OTN. Thus how to map a Lower Order Optical Channel Data Unit (LOODU) to a Higher Order Optical Channel Data Unit (HO ODU) is a focusbeing discussed in the industry. The LO ODU may be ODUk (k=0, 1, 2, 2e,3, 3e) existing in the current OTN, and herein represented as LO ODUk(k=0, 1, 2, 2e, 3, 3e); the HO ODU may be regarded as a datatransmission unit of higher rate, which belongs to the category of theNG OTN and is used for bearing the LO ODU, the corresponding OPU isrepresented as HO OPUk (k=1, 2, 3, 3e, 4).

The conventional technical solution maps the standard ODUj (j=1, 2) (for20 ppm bit tolerance) into the OPUk (k=2, 3) in an asynchronous manner.The asynchronous method maps the ODUj signal into the OPUk through anadjustment policy of −1/0/+1/+2. With the asynchronous manner, a maximumbit error tolerance between ODU1 and OPU2 is −113 to +83 ppm, a maximumbit error tolerance between ODU1 and OPU3 is −96 to +101 ppm, and amaximum bit error tolerance between ODU2 and OPU3 is −95 to +101 ppm.

During the process of implementing the present invention, the inventorfinds that the prior art has at least the following problems:

The method is not suitable for mapping the LO ODU into the HO ODU, e.g.for ODU2c (100 ppm bit tolerance), etc. ODUflex of higher bit tolerancemay occur in the future, and the adjustment policy of −1/0/+1/+2 of theprior art cannot meet the requirement for mapping the LO ODU into the HOODU.

BRIEF SUMMARY OF THE INVENTION

The embodiments of the present invention provide method and apparatusfor mapping and de-mapping in an OTN, so as to map the LO ODU into theHO ODU universally and efficiently.

The embodiments of the present invention provide a mapping method in anOTN, including: (1) constructing an ODTU according to an amount M oftime slots of an HO OPU to be occupied by an LO ODU; (2) mapping the LOODU to a payload area of the ODTU in an M-byte granularity;encapsulating overhead information to the overhead area of the ODTU; and(3) multiplexing the ODTU, which has been mapped the LO ODU andencapsulated with the overhead information, to the HO OPU.

The embodiments of the present invention provide a de-mapping method inan OTN, including: (1) parsing an HO OPU to determine an ODTU and anamount M of time slots occupied by the ODTU; and (2) de-mapping an LOODU from a payload area of the ODTU in an M-byte granularity.

The embodiments of the present invention further provide a mappingapparatus in an OTN, including: (1) a constructing unit, configured toconstruct an ODTU according to an amount M of time slots of an HO OPU tobe occupied by an LO ODU; (2) a mapping unit, configured to map the LOODU to a payload area of the ODTU in an M-byte granularity; (3) anencapsulating unit, configured to package overhead information to theoverhead area of the ODTU; and (4) a multiplexing unit, configured tomultiplex the ODTU, which has been mapped the LO ODU and encapsulatedwith the overhead information, to the HO OPU.

The embodiments of the present invention further provide a de-mappingapparatus in an OTN, including: a parsing unit, configured to parse anHO OPU to determine an ODTU and an amount M of time slots occupied bythe ODTU; and a de-mapping unit, configured to de-map an LO ODU from apayload area of the ODTU in an M-byte granularity.

The technical solutions of the embodiments of the present inventionbring the following beneficial effect: providing a high-efficient anduniversal mode for mapping LO ODU to HO OPU.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to describe the technical solutions of the embodiments of thepresent invention more clearly, the drawings needed for describing theembodiments are introduced briefly as follows. It is apparent that thefollowing drawings are just some embodiments of the present invention,and a person skilled in the art can obtain other drawings based on thesedrawings without paying a creative effort.

FIG. 1 is a flowchart of a mapping method in an OTN according to anembodiment of the present invention;

FIG. 2 is a structural schematic view illustrating dividing an HO OPUinto eight 1.25 G time slots according to an embodiment of the presentinvention;

FIG. 3 is a schematic view illustrating a mapping mode according to anembodiment of the present invention;

FIG. 4 is a schematic view illustrating another mapping mode accordingto an embodiment of the present invention;

FIG. 5 is a schematic view illustrating a mapping from LO ODU to HO OPU2according to an embodiment of the present invention;

FIG. 6 is a schematic view illustrating another mapping from LO ODU toHO OPU2 according to an embodiment of the present invention;

FIG. 7 is a schematic view illustrating another mapping from LO ODU toHO OPU2 according to an embodiment of the present invention;

FIG. 8 is a schematic view illustrating information encoding of“C8M-base+C8M-delta+C8-delta” according to an embodiment of the presentinvention;

FIG. 9 is a flowchart of a de-mapping method in an OTN according to anembodiment of the present invention;

FIG. 10 illustrates a mapping apparatus in an OTN according to anembodiment of the present invention;

FIG. 11 illustrates a mapping apparatus in an OTN according to anotherembodiment of the present invention; and

FIG. 12 illustrates a de-mapping apparatus in an OTN according to anembodiment of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The technical solutions of the embodiments of the present invention areclearly described as follows in conjunction with the drawings of theembodiments. It is apparent that the described embodiments are just apart of embodiments of the present invention, instead of all embodimentsthereof. Based on the embodiments of the present invention, otherembodiments, which are obtained by a person skilled in the art withoutpaying a creative effort, all fall within the protection scope of thepresent invention.

At the data transmitting side, as shown in FIG. 1, a mapping method inan OTN according to an embodiment of the present invention includes: (1)constructing an ODTU according to an amount M of time slots of an HO OPUto be occupied by an LO ODU; (2) mapping the LO ODU to a payload area ofthe ODTU in an M-byte granularity; encapsulating overhead information tothe overhead area of the ODTU; and (3) multiplexing the ODTU, which hasbeen mapped the LO ODU and encapsulated with the overhead information,to the HO OPU, so as to provide an efficient and universal mode formapping the LO ODU to the HO OPU.

For the convenience of understanding the embodiments of the presentinvention, the implementation processes of those embodiments duringspecific applications are described in detail as follows.

The mapping method in an OTN according to an embodiment of the presentinvention includes:

S1: constructing an ODTU according to an amount M of time slots of an HOOPU to be occupied by an LO ODU.

The step includes:

S11: determining the amount M of the time slots of the HO OPU to beoccupied by the LO ODU.

Specifically, the amount M of the time slots of the HO OPU to beoccupied by the LO ODU may be determined according to the rate of the LOODU and the rate of a single time slot of the HO OPU, i.e. M=upperrounding of (the rate of the LO ODU/the rate of a single time slot ofthe HO OPU). For example, HO OPU2 is divided into eight 1.25 G timeslots, and eight frames of HO OPU2 forms a large multi-frame, as shownin FIG. 2. If the rate of a certain LO ODU is assumed as 6 G, then fivetime slots shall be occupied, and M is 5. We can allocate five timeslots to the current LO ODU according to the usage conditions of thetime slots in the HO OPU, herein the five time slots allocated to thecurrent LO ODU are assumed as time slots 2, 3, 5, 7 and 8.

Of course, other methods may also be adopted to determine M and allocatethe time slots to be occupied. Meanwhile, they are not limited by theembodiments of the present invention, and fall within the protectionscope of the embodiments of the present invention.

S12: constructing the ODTU.

The ODTU includes M time slots, and further includes JustificationControl Overhead (JC OH) corresponding to JC OH position of the HO OPU.As shown in FIG. 2, the ODTU includes the time slots 2, 3, 5, 7 and 8 inthe multi-frame formed of eight HO OPUs, and further includes JC OHposition of HO OPU frames to which the respective time slots correspond.The shaded portions in FIG. 2 form corresponding ODTU.

S2: mapping the LO ODU to a payload area of the ODTU in an M-bytegranularity.

The step includes:

S21: determining an amount of LO ODU(s) of M-bytes to be mapped whenmapping in the M-byte granularity, according to an amount X of the LOODU(s) to be transmitted during each multi-frame period, and herein isrepresented as C8M; in another embodiment of the present invention,determining clock information according to the amount X of the LO ODU(s)to be transmitted during each multi-frame period, and herein isrepresented as C8-delta. The above two information is represented as“C8M+C8-delta.”

In which, the method for acquiring X is existing, and hence is notdescribed in the embodiments of the present invention.

Specifically, the embodiment of the present invention may use thefollowing method to determine “C8M−C8-delta”:C8M,MAX=(LO ODU rate*LO ODU maximum frequency deviation)/(M*TS rate*TSminimum frequency deviation)*15232C8M,MIN=(LO ODU rate*LO ODU minimum frequency deviation)/(M*TS rate*TSmaximum frequency deviation)*15232

Where C8M is an integer value with a range of [C8M, MIN lower rounding,C8M, MAX upper rounding]. C8-delta is X−M*C8M, indicating the clockinformation, where X is C8, and C8 is an integer value with a range of[C8, MIN lower rounding, C8, MAX upper rounding].C8,MAX=(LO ODU rate*LO ODU maximum frequency deviation)/(TS rate*TSminimum frequency deviation)*15232C8,MIN=(LO ODU rate*LO ODU minimum frequency deviation)/(TS rate*TSmaximum frequency deviation)*15232

Assuming a certain LO ODU has its X=76111 and occupies M=5 time slots,then C8M=(X/M) lower rounding=15222, C8-delta=X−M*C8M=1. Or C8M=(X/M)lower rounding+1=15223, C8-delta=X−M*C8M=−4. The mapped data informationand clock information can be completely reflected by transmitting theinformation “C8M+C8-delta”, i.e. (15222, 1) or (15223, −4). Thereceiving side may perceive, according to (15222, 1) or (15223, −4),that the transmitting side needs to transmit client data of 76111 bytesduring one multi-frame period, so as to accurately recover the clientclock at the receiving side.

The present invention may also use other methods to determine“C8M+C8-delta”. Meanwhile, they are not limited by the embodiments ofthe present invention, and all fall within the protection scope of thoseembodiments.

S22: mapping the amount of the LO ODU(s) of M-byte to the payload areaof the ODTU in the M-byte granularity.

Mapping in the M-byte granularity means performing one time of mappingoperation of M bytes of client data as a whole; as the above example,mapping the amount of the LO ODU(s) of M-byte to the payload area of theODTU in the M-byte granularity means mapping 15222 or 15223 LO ODUs of5-byte to the payload area of the ODTU, performing the mapping operationevery 5 bytes of LO ODU, and totally mapping for 15,222 or 15,223 times.

Specifically, the sigma-delta algorithm or other Generic MappingProcedure (GMP) mapping methods may be used to map the LO ODU(s) to thepayload area of the ODTU, the other GMP mapping methods meet thefollowing characteristics:

-   -   1. being capable of automatically determining a filling amount        according to the mapped signals and the rate of a target        container;    -   2. being capable of automatically determining distribution        positions of the filling and mapping signals in the target        container according to the mapped signals and the rate of the        target container; and    -   3. transporting position information carrying the filling and        mapping signals in the overhead of the target container.

The characteristic information of the GMP mapping method in theembodiments of the present invention is further described with thefollowing two mapping modes, but is not limited by the two mappingmodes.

Mapping mode 1: evenly distributing filling data and mapping signal datato the payload area through the sigma-delta algorithm. Information suchas positions of the filling and mapping signals is carried andtransported by the overhead of the target container; the effect afterthe mapping is shown in FIG. 3, where S is filling data and D is mappingsignal data; the filling data and the mapping signal data are evenlydistributed to the payload area.

Mapping mode 2: concentratedly placing the filling data in a fixedposition of the payload area, and determining which portions in thepayload area are for the filling data and which portions in the payloadarea are for the mapping signal data according to the filling amount.Information such as positions of the filling and mapping signals iscarried and transported by the overhead of the target container; theeffect after the mapping is shown in FIG. 4, where S is the filling dataand D is the mapping signal data.

S3: encapsulating overhead information to the overhead area of the ODTU;

In an embodiment of the present invention, the overhead informationincludes the amount information of the LO ODU(s) of M-byte, andencapsulating the overhead information to the overhead area of the ODTUincludes: (1) encapsulating the amount information of the LO ODU(s) ofM-byte to the overhead area of the ODTU; (2) Specifically, encapsulatingthe amount information of the LO ODU(s) of M-byte to the overhead areaof the ODTU includes:

directly encapsulating the amount information of the LO ODU(s) of M-byteto the overhead area of the ODTU, and a form of “C8M” may be used; or(3) dividing the amount information of the LO ODU(s) of M-byte into afixed portion of the amount information of the LO ODU(s) of M-bytc and avariable portion of the amount information of the LO ODU(s) of M-byte,and encapsulating the fixed portion of the amount information of the LOODU(s) of M-byte and the variable portion of the amount information ofthe LO ODU(s) of M-byte to the overhead area of the ODTU; transportingin a form of this overhead information may also achieve the same effect.Specifically, a form of “C8M-base+C8M-delta” may be adopted, whereC8M-base+C8M-delta equivalent to C8M, indicating an amount of M-bytes inthe LO ODU(s) mapped to the payload area of the ODTU; C8M-base is anamount of M-bytes in the fixed portion, and C8M-delta is an amount ofM-bytes in the variable portion; or (4) determining amount informationof the LO ODU(s) of M-byte to be filled according to the amountinformation of the LO ODU(s) of M-byte, and encapsulating the amountinformation of the LO ODU(s) of M-byte to be filled to the overhead areaof the ODTU; Transmitting in a form of this overhead information mayalso achieve the same effect; specifically, a form of “S8M” may beadopted, where S represents the filling data, S8M indicates an amount offilled bytes in the ODTU after the LO ODU(s) are mapped to the ODTU, andS8M=15232−C8M.

In another embodiment of the invention, the overhead informationincludes the amount information of the LO ODU(s) of M-byte and the clockinformation, encapsulating the overhead information to the overhead areaof the ODTU includes: encapsulating the amount information of the LOODU(s) of M-byte and the clock information to the overhead area of theODTU.

Specifically, encapsulating the amount information of the LO ODU(s) ofM-byte and the clock information to the overhead area of the ODTUincludes: (1) directly encapsulating the amount information of the LOODU(s) of M-byte and the clock information to the overhead area of theODTU, and a form of “C8M+C8-delta” may be used; or (2) dividing theamount information of the LO ODU(s) of M-byte into a fixed portion ofthe amount information of the LO ODU(s) of M-byte and a variable portionof the amount information of the LO ODU(s) of M-byte, and encapsulatingthe fixed portion of the amount information of the LO ODU(s) of M-byteand the variable portion of the amount information of the LO ODU(s) ofM-byte to the overhead area of the ODTU; transporting in a form of thisoverhead information may also achieve the same effect; specifically, aform of “C8M-base+C8M-delta+C8-delta” may be used, whereC8M-base+C8M-delta equivalents to C8M, indicating an amount of M-bytesin the LO ODU(s) mapped to the payload area of the ODTU; C8M-base is anamount of M-bytes in the fixed portion, and C8M-delta is an amount ofM-bytes in the variable portion; or (3) determining amount informationof the LO ODU(s) of M-byte to be filled according to the amountinformation of the LO ODU(s) of M-byte, and encapsulating the amountinformation of the LO ODU(s) of M-byte to be filled to the overhead areaof the ODTU; transporting in a form of this overhead information mayalso achieve the same effect; specifically, a form of “S8M+S8-delta” maybe adopted, where S represents the filling data, S8M indicates an amountof filled bytes in the ODTU after the LO ODU(s) are mapped to the ODTU,S8M=15232−C8M, and S8-delta indicates the clock information.

Encapsulating the overhead information to the overhead area of the ODTUincludes: encapsulating the overhead information to an overheadcorresponding to a first time slot or a last time slot in the ODTU.

The overhead information indicates clock information and an amount ofthe LO ODU(s) of M-byte mapped to the ODTU in next n multi-frames, orindicates clock information and an amount of the LO ODU(s) of M-bytemapped to the ODTU in next n frames, where n is a natural number.

In an embodiment of the present invention, the “C8M+C8-delta”information indicates conditions of the clock information and an amountof M-bytcs in the LO ODU(s) mapped to the ODTU in the next multi-frame.

If the “C8M+C8-delta” information is encapsulated to the JC OHcorresponding to the first time slot in the ODTU, i.e. the JC OHposition of the 2^(nd) frame of HO OPU corresponding to the time slot 2in the current multi-frame, then the mapping process is shown in FIG. 5.If the “C8M+C8-delta” information is encapsulated to the JC OHcorresponding to the last time slot in the ODTU, i.e. the JC OH positionof the 8^(th) frame of HO OPU corresponding to the time slot 8 in thecurrent multi-frame, then the mapping process is shown in FIG. 6.

In another one embodiment of the invention, the“C8M-base+C8M-delta+C8-delta” information indicates conditions of theclock information and an amount of M-bytes in the LO ODU(s) mapped tothe ODTU in the next frame of HO OPU.

Also taking HO OPU2 as an example, in the embodiment, as shown in FIG.7, encapsulating “C8M-base+C8M-delta+C8-delta” to the JC OH positions ofthe 2^(nd), 3^(rd), 5^(th), 7^(th) and 8^(th) frames of HO OPU2corresponding to time slots 2, 3, 5, 7 and 8 in the current multi-frame,respectively. The information “C8M-base+C8M-delta+C8-delta” at the2^(nd), 3^(rd), 5^(th), 7^(th) and 8^(th) frames of HO OPU2 indicateclock information and amounts of M-bytes in the LO ODU(s) mapped to thepayload area of the ODTU in the next frame of HO OPU2, respectively. Theamount of M-bytes in the LO ODU(s) mapped to the payload area of theODTU in other frames of HO OPU2 is C8M-base; i.e. indicating mappingC8M-base+C8M-delta M-byte data of the LO ODU(s) in an M-byte granularityto the ODTU payload areas in the 3^(rd), 4^(th), 6^(th) and 8^(th)frames of HO OPUs in the current multi-frame and the ODTU payload areain the 1^(st) frame of HO OPU in the next multi-frame. Mapping C8M-baseM-byte data of the LO ODU(s) in an M-byte granularity to the ODTUpayload areas in the 2^(nd), 5^(th) and 7^(th) frames of HO OPUs.

In the embodiment of the present invention, the information“C8M-base+C8M-delta C8-delta” may be encapsulated in the following mode,but not limited thereby, as shown in FIG. 8.

In which, C8M-base occupies 13 bits, C8M-delta occupies 3 bits, C8-deltaoccupies 8 bits, and FEC occupies 8 bits; herein the FEC errorcorrecting function is added, and an encoding mode of BCH (16, 12) maybe used to achieve an effect of correcting an error of lbit, and improvethe reliability of the information “C8M-base+C8M-delta+C8-delta” duringtransportation. In addition, the FEC may also be replaced by CRC, andthe information “C8M-base+C8M-delta+C8-delta” received at the receivingside is ensured as correct through a CRC verification.

S4: multiplexing the ODTU, which has been mapped the LO ODU andencapsulated with the overhead information, to the HO OPU.

The mapping method in an OTN according to the embodiment of the presentinvention not only provides a high-efficient and universal mode formapping the LO ODU to the HO OPU, compatible with processes of mappingLO ODU to HO OPU in different granularities for the convenience ofinterconnection, but also separates the data information from the clockinformation to mapping in a large granularity, and carries the clockinformation with the byte granularity to solve the problem of poorperformance of clock recovered at the receiving side caused by mappingonly with large granularity.

Correspondingly, at the data receiving side, as shown in FIG. 9, theembodiment of the present invention further provides a de-mapping methodin an OTN, for parsing an HO OPU to determine an ODTU and an amount M oftime slots occupied by the ODTU; and de-mapping an LO ODU from a payloadarea of the ODTU in an M-byte granularity.

De-mapping the LO ODU from the payload area of the ODTU in the M-bytegranularity includes: (1) acquiring information of an amount of the LOODU of M-byte from the overhead of the ODTU; and (2) de-mapping theamount of the LO ODU of M-byte from the payload area of the ODTU in theM-byte granularity.

Dc-mapping the LO ODU of M-byte from the payload area of the ODTU in theM-bytc granularity further includes: acquiring clock information fromthe overhead of the ODTU, and recovering the clock of client serviceaccording to the clock information.

As shown in FIG. 10, the embodiment of the present invention furtherprovides a mapping apparatus in an OTN, including: (1) a constructingunit, configured to construct an ODTU according to an amount M of timeslots of an HO OPU to be occupied by an LO ODU; (2) a mapping unit,configured to for map the LO ODU to a payload area of the ODTU in anM-byte granularity; (3) an encapsulating unit, configured to encapsulateoverhead information to the overhead area of the ODTU; and (4) amultiplexing unit, configured to multiplex the ODTU, which has beenmapped the LO ODU and encapsulated with the overhead information, to theHO OPU.

As shown in FIG. 11, another embodiment of the present inventionprovides a mapping apparatus in an OTN, including the constructing unit,the mapping unit, the encapsulating unit and the multiplexing unit asshown in FIG. 10, where the mapping unit includes: (1) a determiningmodule, configured to determine an amount of the LO ODU of M-byte to bemapped when mapping in an M-byte granularity, according to an amount Xof the LO ODU to be transmitted in each multi-frame period; (2) amapping module, configured to map the amount of the LO ODU of M-byte tothe payload area of the ODTU in the M-byte granularity; and (3) theencapsulating unit is configured to encapsulate the amount informationof the LO ODU of M-byte to the overhead area of the ODTU.

In another embodiment of the present invention, the determining moduleis further adopted for determining clock information according to theamount X of the LO ODU to be transmitted during each multi-frame period;and the encapsulating unit is further configured to encapsulate theclock information to the overhead area of the ODTU.

As shown in FIG. 12, the embodiment of the present invention furtherprovides a de-mapping apparatus in an OTN, including: (1) a parsingunit, configured to parse an HO OPU to determine an ODTU and an amount Mof time slots occupied by the ODTU; and (2) a de-mapping unit,configured to de-map an LO ODU from a payload area of the ODTU in anM-byte granularity.

The detailed contents about signal processing and executions among thecomponents of the above apparatuses are based on the same concept of themethod embodiments of the present invention, please refer to thedescriptions of the method embodiments of the present invention, andherein are not described.

The above descriptions are just some exemplary embodiments of thepresent invention, and the protection scope of the present invention isnot limited thereby. Any modification or substitution that can be easilyconceived by a person skilled in the art within the technical scopedisclosed by the present invention shall be covered by the protectionscope of the present invention. Therefore, the protection scope of thepresent invention shall be subject to that of the claims.

The invention claimed is:
 1. A mapping method used in an OpticalTransport Network (OTN), comprising: constructing an Optical ChannelData Tributary Unit (ODTU) according to an integer value M larger than1, wherein the integer value M equals the number of time slots of a HighOrder Optical Channel Payload Unit (HO OPU) that are to be occupied bydata of a Low Order Optical Channel Data Unit (LO ODU) via the ODTU;mapping the data of the LO ODU into a payload area of the ODTU bymapping the data of the LO ODU in units of M bytes, such that multipleunits of M bytes are mapped into the payload area of the ODTU;encapsulating overhead information to an overhead area of the ODTU; andmultiplexing the ODTU, into which the data of the LO ODU has been mappedand to which the overhead information has been encapsulated, to the HOOPU.
 2. The method according to claim 1, wherein the overheadinformation comprises information indicating an amount Y of M-byte dataunits of the LO ODU which are transmitted during a multi-frame period.3. The method according to claim 2, wherein the overhead informationfurther comprises clock information that is determined according to anamount of data of the LO ODU required to be transmitted during themulti-frame period and the amount Y.
 4. The method according to claim 3,wherein the encapsulating the overhead information to the overhead areaof the ODTU comprises at least one of the group consisting of: (a)encapsulating information of the amount Y to the overhead area of theODTU; (b) dividing information of the amount Y into information of afixed portion of the amount Y and information of a variable portion ofthe amount Y, and encapsulating the information of the fixed portion ofthe amount Y and the information of the variable portion of the amount Yto the overhead area of the ODTU; and (c) determining an amount ofM-byte filling data to be filled according to the amount Y, andencapsulating information of the amount of the M-byte filling data to befilled to the overhead area of the ODTU.
 5. The method according toclaim 2, wherein the encapsulating the overhead information to theoverhead area of the ODTU comprises at least one of the group consistingof: (a) encapsulating information of the amount Y to the overhead areaof the ODTU; (b) dividing information of the amount Y into informationof a fixed portion of the amount Y and information of a variable portionof the amount Y, and encapsulating the information of the fixed portionamount Y and the information of the variable portion of the amount Y tothe overhead area of the ODTU; and (c) determining an amount of M-bytefilling data to be filled according to the amount Y, and encapsulatinginformation of the amount of the M-byte filling data to be filled to theoverhead area of the ODTU.
 6. The method according to claim 1, whereinafter the multiplexing, the overhead information is presented in anoverhead area corresponding to the first time slot or the last time slotamong time slots occupied by the ODTU in a multi-frame.
 7. The methodaccording to claim 1, wherein the overhead information is multiplexed toa current multi-frame comprising multiple HO OPU frames and comprisesamount information indicating an amount of M-byte data units of the LOODU which are mapped to an ODTU in next n multi-frame, wherein n is anatural number.
 8. The method according to claim 1, wherein mapping thedata of the LO ODU into the payload area of the ODTU is realized byusing a sigma-delta algorithm.
 9. The method according to claim 1,wherein mapping the data of the LO ODU into the payload area of the ODTUis realized by using a Generic Mapping Procedure (GMP) mapping method,and said GMP mapping method meets the following characteristics:automatically determining a filling amount according to mapped signalsand a rate of target container; automatically determining distributionpositions of filling and mapping signals in the target containeraccording to the mapped signals and the rate of target container; andtransporting position information carrying the filling and mappingsignals in the overhead of the target container.
 10. The methodaccording to claim 1, wherein the overhead information comprises firstoverhead information indicating a fixed portion of an amount Y of M-bytedata units of the LO ODU and second overhead information indicating avariable portion of the amount Y; wherein the number of M-byte dataunits which are multiplexed in a first HO OPU frame allocated to the LOODU is indicated by a combination of the first overhead information andthe second overhead information; wherein the number of M-byte data unitswhich are multiplexed in a second HO OPU frame allocated to the LO ODUis indicated by the first overhead information without the secondoverhead information.
 11. A mapping apparatus used in an OpticalTransport Network (OTN), comprising: a constructing unit, configured toconstruct an Optical Channel Data Tributary Unit (ODTU) according to aninteger value M larger than 1, wherein the integer value M equals thenumber of time slots of a High Order Optical Channel Payload Unit (HOOPU) that are to be occupied by data of a Low Order Optical Channel DataUnit (LO ODU) via the ODTU; a mapping module, configured to map the dataof the LO ODU into a payload area of the ODTU by mapping the data of theLO ODU in units of M bytes, such that multiple units of M bytes aremapped into the payload area of the ODTU; an encapsulating unit,configured to encapsulate overhead information to an overhead area ofthe ODTU; and a multiplexing unit, configured to multiplex the ODTU, towhich the data of the LO ODU has been mapped and to which the overheadinformation has been encapsulated, to the HO OPU.
 12. The apparatusaccording to claim 11, wherein the overhead information comprisesinformation indicating an amount of M-byte data units of the LO ODUwhich are transmitted during a multi-frame period.
 13. The apparatusaccording to claim 11, further comprising: a determining module,configured to determine clock information according to an amount of dataof the LO ODUs to be transmitted during the multi-frame period; andwherein the encapsulating unit is configured to encapsulate the clockinformation to the overhead area of the ODTU.
 14. The apparatusaccording to claim 11, further comprising: a determining module,configured to determine an amount Y of M-byte data units of the LO ODUduring a multi-frame period; wherein the encapsulating unit isconfigured to encapsulate information indicating the amount Y to theoverhead area of the ODTU.
 15. The apparatus according to claim 11,wherein the overhead information comprises first overhead informationindicating a fixed portion of an amount Y of M-byte data units of the LOODU and second overhead information indicating a variable portion of theamount Y; wherein the number of M-byte data units which are multiplexedin a first HO OPU frame allocated to the LO ODU is indicated by acombination of the first overhead information and the second overheadinformation; wherein the number of M-byte data units which aremultiplexed in a second HO OPU frame allocated to the LO ODU isindicated by the first overhead information without the second overheadinformation.